The present invention is a passive acoustic system for supplying the direction and the distance of a source, called noise emitter, emitting sound signals. These systems are principally used by submarines for, after detecting one or several noise emitters, following same. This information is then used for controlling a weapons system.
Determining the direction and the distance of a noise emitter is known, using three aligned generally equidistant receivers.
The signals received by the end receivers are each applied to a correlation circuit which further receives the signal from the central receiver. The two intercorrelation signals each pass through a time maximum which supplies the algebraic value of the delay of the two signals received by the end receivers with respect to the signal received by the central receiver.
A computing circuit determines from these delay values the direction and distance of the noise source.
The accuracy obtained for the parameters measured depends on the ratio of the signal emitted by a noise source, in a certain frequency band, and the power of the noise, other than the useful signal, in this same frequency band. This ratio is called signal to noise ratio.
It is known, that to increase the signal to noise ratio (S/N) in passive acoustic systems, to use as receivers an array of transducers or hydrophones. The S/N ratio at the output of the sound transducers is thus increased by the gain with respect to the S/N ratio at the input of each hydrophone.
For example, in certain commercially available systems, each receiver array is formed of several columns of several hydrophones. On each side of the submarine are also disposed three arrays covering two angular sectors of 120.degree., on the port side and on the starboard side. Each array allows several directional beams to be formed.
In submarines equipped with a passive system, in the prior art, there is generally provided in addition a passive monitoring system. The passive monitoring signals are processed so as to preform beams of an angular width of a few degrees and it is the passive monitoring system which supplies in this case the direction of the noise source.
The need to preform beams both for the telemetry system and for the passive monitoring system presents the drawback of being of great complexity.
The system in accordance with the invention remedies this disadvantage because it does not comprise formation of beams signals supplied by the receivers of the passive acoustic range measurement system. The reduction of the noise ratio which results therefrom is compensated for, at least partially, in accordance with the invention, by using in combination signals from these receivers and those supplied by the passive monitoring system, using the preformed directional path information of a passive monitoring system.